Residual Strength Characteristics Research Articles

Statistical Damage Constitutive Model for Cemented Sand considering the Residual Strength and Initial Compaction Phase

Based on continuum damage mechanics and the assumption of volume invariance, a damage constitutive model of cemented sand under triaxial stress was established while considering residual strength. Statistical theory was then introduced into this model. Assuming that the microunit strength of cemented sand obeys a Weibull random distribution, an expression of microunit strength based on the Mohr–Coulomb criterion was derived. Additionally, a damage evolution equation and a statistical damage constitutive model of cemented sand under triaxial stress were established. In order to consider the nonlinear deformation and volume change in the initial pore compaction stage, the critical point reflecting the completion of the initial compaction stage was determined. This was done by applying the volume invariance assumption to the linear portion of the stress and strain curve and performing a coordinate transformation. The nonlinearity of the initial compaction stage was fitted by a quadratic function. A triaxial compression test of cemented sand was then carried out to verify this proposed method. The results show that the calculated values by the damage constitutive model fit well with the actual experimental values and that the calculated results can reflect the stress softening, residual strength, and initial compaction characteristics of cemented sand, which shows the rationality and feasibility of the model.

Experimental study of residual strength and the index of shear strength characteristics of clay soil

Using a ring shear apparatus, the variation in the residual strength characteristics of 21 groups of saturated clay soil samples were experimentally investigated, and the results are discussed in this paper. The clay soil samples had different plasticity indexes under 10 different consolidation conditions. The influences of shear rate, over-consolidation ratio, plasticity index, and multi-stage shear mode on the residual strength were investigated. New shear strength variation trend data and a corresponding equation for shear strength calculations as a function of plasticity index of soils under large deformation are presented. The experimental results indicate that 1) both the shear rate and over-consolidation ratio have a negligible influence on the residual strength; 2) the residual strength gradually decreases as the plasticity index increases; 3) the residual strength shows a significant nonlinearity with the normal stress when subjected to low- or high-levels of normal stress; 4) the internal friction angle of drained clay decreases as the plasticity index increases under large deformation. Finally, a formula is proposed to describe the relationship between the residual inner friction angle and plasticity index.

Acoustic emission method to study fracture (Mode-I, II) and residual strength characteristics in composite-to-metal and metal-to-metal adhesively bonded joints

ABSTRACTFailure behaviour of two types of adhesively bonded joints (composite-to-metal, metal-to-metal) has been studied under failure modes (Mode I: double cantilever beam (DCB) and Mode II: three-point end notch flexures (3-ENF)) using acoustic emission (AE) technique. The bonded specimens were prepared using two types of adhesive bond materials with three variations of adhesive bond quality. The effect of the presence of interfacial defects along the interface on the residual strength of the joint has also been studied. It was possible using the maximum AE amplitude method to select the AE events of mechanical significance. However, it proved difficult to propose a definitive AE trait for the mechanical phenomena occurring within specific AE event signals, for all adhesive types, bond qualities, and substrate configurations, therefore, all specimen combinations. There was a notable shift in spectral energy proportion as the AE source of mechanical significance varied along the specimen length for specimen combinations. However, it was difficult to confirm this distinctive trait for all specimen combinations due to difficulty in confirming the location and exact mechanical source. The proposed measurement technique can be useful to assess the overall structural health of a bonded system and may allow identification of defects.

Temperature‐dependent residual shear strength characteristics of smectite‐bearing landslide soils

AbstractThis paper presents experimental investigations regarding the effect of temperature on the residual strength of landslide soils at slow‐to‐moderate shearing velocities. We performed ring‐shear tests on 23 soil samples at temperatures of 6–29°C. The test results show that the shear strength of smectite‐rich soils decreased when temperatures were relatively low. These positive temperature effects (strength losses at lower temperatures) observed for smectite‐bearing soils are typical under relatively slow shearing rates. In contrast, under relatively high shearing rates, strength was gained as temperature decreased. As rheological properties of smectite suspensions are sensitive to environmental factors, such as temperature, pH, and dissolved ions, we inferred that temperature‐dependent residual strengths of smectitic soils are also attributed to their specific rheological properties. Visual and scanning electron microscope observations of Ca‐bentonite suggest that slickensided shear surfaces at slow shearing rates are very shiny and smooth, whereas those at moderate shearing rates are not glossy and are slightly turbulent, indicating that platy smectite particles are strongly orientated at slow velocities. The positive temperature effect is probably due to temperature‐dependent microfriction that is mobilized in the parallel directions of the sheet structure of hydrous smectite particles. On the contrary, the influence of microviscous resistance, which appears in the vertical directions of the lamination, is assumed to increase at faster velocities. Our results imply that if slip‐surface soils contain high fractions of smectite, decreases in ground temperature can lead to lowered shear resistance of the slip surface and trigger slow landslide movement.

Ring shear characteristics of discontinuous plane

Residual shear strength is an essential parameter in evaluating the long-term stability of reactivated landslides in geotechnical engineering. According to previous studies, earthquake-induced landslides may occur on discontinuous planes, such as bedding planes, between weathered and unweathered mudstones having different cementation properties resulting from diagenesis. However, the shear behaviour at the contact surfaces between the cemented and the non-cemented soil layers has not yet been sufficiently investigated. The objective of this study is to elucidate the residual strength characteristics of artificial bedding planes that model the actual behaviour of slip surfaces occurring between two layers with different degrees of cementation. The experimental tests were conducted with a ring shear test apparatus. Additionally, in order to simulate the realistic mechanical behaviour of naturally cemented clay, artificial cementation bonds were created by adding a cementing agent at different ratios to clay slurry. A series of ring shear tests was performed under various conditions on one-layer non-cemented and cemented kaolin samples, respectively, as well as on two-layer specimens composed of one layer each of cemented kaolin and non-cemented kaolin. The test results showed that the residual friction angle of the two-layer combinations of non-cemented and cemented kaolin was approximately 33.6% lower than that of pure kaolin. In contrast, the residual friction angle of cemented kaolin may be as much as 6.2° greater than that of non-cemented kaolin. At cement ratios of up to 2%, the stress ratio of cemented kaolin increased as the shear displacement rate increased. As the cement content was increased beyond 2%, the degree of increase was not significant. These results suggest that the residual strength of cemented kaolin at cement contents greater than 2% is independent of the shear rate.

Residual Strength Characteristics of Polymer Fibre Concrete Exposed to Elevated Temperature

Mechanical properties of polymer based concrete exposed to high temperature effects are evaluated in the present study. Concrete mixtures were prepared using SBR (styrene butadiene rubber) latex and reinforced with polypropylene fibres (PP). Latex polymer modified concrete mixes consisting of different aggregate proportions and polymeric fibre contents (0.1 to 0.3% Vf) were investigated for high temperature performance. Concrete specimens after required curing were subjected to different high temperature effects from 200°C to 800°C and the corresponding weight loss and residual strength was determined. In addition, the residual elastic modulus of polymer concretes was determined from the compressive stress-strain properties. Experimental observations showed that, compared to plain concrete the residual strength characteristics of polymer fibre concretes were affected when exposed to high temperature. Strength degradation occurred with increase in temperature and the test results indicated that the temperature sustainability of polypropylene fibre concretes were observed up to 200°C. A maximum compressive strength loss upto 56.75% for plain concrete and 9.87% for polymer fibre concrete was noticed when exposed to high temperature upto 800°C. Further, microscopic analysis of fibre concretes exposed to high temperature showed possible melting of PP fibres resulting in filling the pore spaces which possibly improved the matrix hardening. Also, the high volume fibre incorporated concrete mixes showed maximum residual strength gain due to favourable matrix strengthening and demonstrated high temperature performance of polymer concretes.

Residual strength of corroded subsea pipelines subject to combined internal pressure and bending moment

Subsea pipelines used for oil and gas production in deepwater are exposed to harsh environment involving corrosion, high internal pressure, high temperature, and bending moment. Failure of subsea pipelines can cause serious problems, including oil/gas spill, hydrocarbon explosion and fires, production downtime, and maintenance and repair. Hence, it is of paramount importance to prevent failure of subsea pipelines. The aim of the present study is to investigate the residual strength characteristics of corroded subsea pipelines under combined internal pressure and bending moment. ANSYS non-linear finite element method was applied to examine the residual strength characteristics of subsea pipelines by varying the corrosion damage and the loading ratio of internal pressure and bending moment, where the size of the corrosion damage was also varied. The ultimate strength interaction relationships of subsea pipelines between the internal pressure and bending moment with various corrosion damages were also developed. Finally, the insights and conclusions of the present study were summarised.

Effects of Temperature Levels and Concrete Cover Thickness on Residual Strength Characteristics of Fire Exposed Reinforced Concrete Beams

Reinforced concrete structures are often subjected to fire of various degrees. After fire if the structure does not collapse during the fire there is need for post-fire assessment of its structural integrity before the fate of the structure can be determined. With the knowledge of the temperature of the fire, thickness of concrete cover, residual strength of concrete and tensile strength of embedded reinforcement after fire exposure, we can predict the residual carrying capacity of the beams after fire. The experimental procedure involves some specimens of reinforcing steel bars (∅16mm) enclosed in varying concrete covers in concrete beams which were exposed to ISO 834 furnace temperatures for 2hrs. After fire, the steel bars were removed and tested for tensile strength characteristics and the reduction in strength trend compared with the current code predictions for stress strain relationship of hot-rolled reinforcing steels at elevated temperatures. The variation in the residual moment and shear capacities of the reinforced concrete beams with temperature were evaluated. The experimental residual strength index was found to be greater than the theoretical prediction in the code. The variation in cover thickness of concrete to embedded reinforcement in beams was also noticed to be of no significance to the post-fire tensile strength of the steel reinforcement if the fire temperature is below 700oC. Keywords: Post-fire, flexure, residual strength, concrete cover, tensile strength, iso834 fire.

Residual Ultimate Strength of Box Girders with Variable Cracks

The aim of the present study is to investigate the residual ultimate strength characteristics of box girders with variable cracks under torsional loading. A series of finite element models are established by changing the crack length and crack angle using a commercial FEA program, ABAQUS. The cracks are located at the center and torques are applied on both ends of the box beam. Different aspect ratios are considered to evaluate the effects of cracks on box beams for various widths and lengths of panels in the middle yielding region. The accuracy of the nonlinear FEA results is verified by a comparison with previous predicted formulas. Based on the FEA results, the relationship between the residual ultimate strength and crack parameters can be indicated in a function with period of in the form of Fourier series.

Peak and residual strength characteristics of cement-treated soil cured under different consolidation conditions

The shear strength of cement-treated soil can be changed by both cementation and consolidation during the early stages of hardening because of cement hydration. Based on the results of triaxial and unconfined compression tests, this paper describes the effects of isotropic and one-dimensional consolidation stress, applied during the curing period, on the undrained peak and residual shear strengths of cement-treated soil. The sample used was a mixture of fine-grained sand and ordinary Portland cement. A consolidated undrained triaxial compression test (ICU) was conducted on the specimens immediately after the cement treatment. Each test was conducted under different consolidation pressures, curing times and delayed loading times. The following conclusions were developed from the results and discussions: (1) the undrained peak shear strength of cement-treated soil, cured under different consolidation conditions, increases with an increase in either the consolidation pressure or the curing time, whereas it gradually decreases with an increase in the delayed loading time. (2) The rate of undrained strength increase resulting from consolidation differs significantly between isotropic and one-dimensional consolidations. (3) For a curing time of between one and seven days, the rate of strength increase by isotropic consolidation exceeds that by one-dimensional consolidation. The simultaneous volumetric change of cement-treated soil during consolidation depends on the stress conditions of the specimen, that is, the difference between isotropic and one-dimensional consolidations. (4) When the test is not conducted under nearly in-situ conditions, the undrained shear strength may be underestimated, depending on the time interval between the cement treatment and the start of consolidation. (5) The shear strength in the residual state is influenced by the consolidation pressure during curing. (6) As the consolidation pressure during curing increases, the specimens exhibit a higher residual strength.

Prediction of post-impact residual strength and fatigue characteristics after impact of CFRP composite structures

The residual strength and fatigue life of CFRP (Carbon Fiber-Reinforced Plastic) composite structures with impact damage were predicted by using the characteristic length of the composite with the hole corresponding to the impact damage area. Since the specimen has a C-shaped structure that is different from the shape of a standard specimen, the shape factor was obtained from the concentration of the plate specimen and that of the structure using finite element analysis. The fatigue life of composite structures with impact damage can be predicted accurately by applying the prediction model, which takes into account the residual strength after impact, the shape factor which considers geometric characteristics, and the fatigue characteristics of virgin composites that have not been impacted to the model for strength degradation following impact.

Evaluation for residual strength and fatigue characteristics after impact in CFRP composites

In this study, the residual strength characteristics of woven carbon–fiber-reinforced plastic (CFRP) composites were evaluated according to variations of the impact energy as well as the diameter of the impactor, by conducting tensile tests on impacted specimens. Then, a prediction model for the residual strength after impact was proposed, which the damaged area is replaced with an equivalent hole notch. Fatigue tests were also conducted for CFRP specimens after impact, and a prediction model for the fatigue life was proposed and verified with fatigue test results. The results of the prediction equation for residual strength after impact agree well with the experimental results. The results predicted by the fatigue life equation proposed using the incident impact energy are slightly above the boundary of the test results, but the results using the absorbed impact energy agree well with the fatigue test results.

Notched GFRP: anisotropy, residual strength, and fracture characteristics

This research aims to analyze a study of the mechanical response, in the presence of geometric discontinuity, of glass fiber-reinforced plastics to the uniaxial tensile test. Geometric discontinuity is characterized by a circular hole in the longitudinal section (with reduction of the cross-section) of the composite. In this study, different configuration types are tested, with and without hole, to provide a better understanding of the mechanical properties, with respect to residual strength, anisotropy, and fracture characteristics. The residual strength determined using the precepts given by the ASTM D 5766-07 standard is used in the point-stress criterion and average-stress criterion failure theories for the semi-empirical calculation of the distances ( d0 and a0) in the vicinity of the hole, the region where stress failure occurs. Semi-empirical distances are determined for the composite laminate whose configuration is considered isotropic. The results show the direct influence of the presence of geometric discontinuity and residual strength in all the parameters studied, in addition to fracture characteristics.

Effects of Thermal Loading Conditions on the Mechanical Properties of S45C/Cu/Si3N4 Composites

The effects of thermal loading conditions on the mechanical properties of S45C/Cu/Si3N4 composites with brazing filler metals of AgCu and AgCuTi are described. Thermal loading tests were conducted on test samples under various heat conditions, after which the joint parts of the samples were observed with a focus on the Cu interlayers using an optical microscope. Four-point bending tests were conducted on the samples to evaluate the residual strength and stress strain characteristics of the samples. In addition, fracture surfaces and the origins of the fractures were observed using an optical microscope. The results showed that thermal loading of the S45C/Cu/Si3N4 composites caused fatigue damage to the Cu interlayers and its amount increased with increases in the cycle number and temperature range of thermal loading. In the case of relatively-mild thermal loading conditions, fracture initiation regions were observed at the Cu/Si3N4 boundary. In contrast, fracture initiation regions were observed in the Cu interlayer for the samples subjected to relatively-extreme thermal loading conditions. The increases in the cycle number and temperature range of thermal loading promoted reductions of residual strength, resilient modulus and residual fracture ductility for the samples. The reductions of the mechanical properties of the S45C/Cu/Si3N4 composites were affected by the fatigue damage of the Cu interlayers. It was concluded that continuous operation (no start-stop system) is suitable for long-term use of ceramic/metal composites including interlayers in order to minimize reduction of their mechanical strength.

Study on the Deformation and Strength Characteristics of Geotechnical Grille Reinforced Sand-Gravel under Low Confining Pressure

A series of large scale consolidated drained shear triaxial tests were performed on reinforced and unreinforced sand-gravel specimens, the peak strength and residual strength characteristics of reinforced and unreinforced sand-gravel specimens were compared. The results show that: the peak strength, the residual strength and cohesion of reinforced sand-gravel are higher than unreinforced specimens, and is related to the characteristics of geotechnical grille used in this study. However, adding geotechnical grille has less effect on maximum volumetric strain and internal friction angle of sand-gravel.

Residual ultimate strength of structural members with multiple crack damage

This paper highlights the importance of residual ultimate strength in aging structures with multiple cracking damage and suggests simplified models for predicting the ultimate strength of multi-cracked structural members. Nonlinear finite element methods are employed to investigate the residual ultimate strength characteristics of these members when they have both a ‘lead crack’ and several ‘disturbing cracks.’ The link-up mechanism between lead and disturbing cracks at the plastic zones in terms of the ligament is illustrated. The effects of the location and size of the disturbing cracks when the lead crack is dealt with as a primary parameter of influence are investigated. It is found that when these disturbing cracks are near the lead crack, they reduce the ultimate strength of the structural members. However, their effect is negligible when they are located in a low-stress region of these members. A number of important insights drawn from the study presented herein are documented.

Residual ultimate strength of steel plates with longitudinal cracks under axial compression—Nonlinear finite element method investigations

The main objective of the present paper is to numerically examine the residual ultimate strength characteristics of steel plates with longitudinal cracks under axial compressive actions. The present paper is a sequel to the author's previous paper [Paik, J.K., 2008. Residual ultimate strength of steel plates with longitudinal cracks under axial compression—Experiments. Ocean Engineering 35, 1775–1783]. In contrast to the previous paper, the present paper deals with nonlinear finite element method investigations. Because the test programme is usually limited to a few test models in number for many reasons, the application of nonlinear finite element methods is often more beneficial to handle a more variety of parameters of influence. In the present paper, the insights developed from a series of ANSYS nonlinear finite element method computations are documented, where the effects of the crack orientation, the crack location, the crack size, the plate thickness, and the plate aspect ratio on the residual ultimate strength of steel plates with longitudinal cracks under axial compression are discussed. The insights developed from the present work will be useful for cracking damage-tolerant design of steel-plated structures and also for health monitoring or condition assessment of aging steel-plated structures with cracking damages.

Residual ultimate strength of steel plates with longitudinal cracks under axial compression–experiments

The main objective of the present study is to examine the residual ultimate strength characteristics of steel plates with cracking damages under axial compressive actions through experimental investigations. The present study is a sequel of the author's previous paper (Paik, J.K., Satish Kumar, Y.V., Lee, J.M., 2005. Ultimate strength of cracked plate elements under axial compression or tension. Thin-Walled Structures, 43, 237–272). In contrast to the previous paper which dealt with transverse cracks located in the direction normal to the axial loading direction, the present paper is concerned with longitudinal cracks which are located in parallel to the axial loading direction. Similar to the previous paper, the orientation/location and size of cracks inside the plates are varied for the present experimental investigations. The details of experimental results are documented. The database and insights developed from the present work will be useful for cracking damage-tolerant design of steel-plated structures and also for condition assessment or health monitoring of aging steel-plated structures.

Residual Strength Characteristics of Naturally and Artificially Cemented Clays in Reversal Direct Box Shear Test

The naturally cemented clay preserving chemical bonds that was gradually disintegrated by weathering is a soil exhibiting a progressive failure such as a landslide. The residual strength of soil possessing cementation properties given by diagenesis has not yet been investigated. The objective of this study is to clarify the residual strength characteristics of naturally and artificially cemented clays using an improved reversal direct box shear test apparatus. Based on the test results of reconstituted Kaolin clay, undisturbed, remolded and reconstituted samples of three natural clays, this paper describes the influence of normal stress, shear displacement rate, consolidation and shear histories on the residual strength of cemented clay. Especially, to simulate the same mechanical behavior as the naturally cemented clays, the cementation was artificially reproduced by adding cementing agents to slurry clay. Consequently, 1) the residual strength of cemented clay is independent of consolidation yield stress and initial void ratio. 2) The residual strength of cemented clay as well as non-cemented clay increases with increasing the shear displacement rate. 3) The residual strength of cemented clay as well as non-cemented clay is not affected by any stress history.

Response surface characterization of the mechanical behavior of impact-damaged sandwich composites

In this research, Response Surface Methodology (RSM) is employed to characterize the influence of material configuration on the damage tolerance and residual strength characteristics of sandwich composites. Test specimens used were comprised of carbon-epoxy woven fabric facesheets, and Nomex honeycomb cores. The ranges of the material configuration used are typical of those employed in aircraft applications. A series of carefully selected tests were used to isolate the coupled influence of various combinations of the number of facesheet plies, core density, and core thickness on the damage formation and residual strength degradation due to normal impact. Response surface estimates suggest that impact damage development and residual strength degradation are highly material and lay-up configuration dependent. Increasing the core thickness for a specific number of facesheet plies resulted in decreasing the impact damage, whereas increasing the number of facesheet plies for a given core thickness resulted in enhancing the residual strength. The derived damage tolerance and residual strength models can lead to a better understanding of the mechanical behavior of the impact-damaged sandwich composites, and hence improve their design and expand their applications.